We update the social share counts in fixed time intervals, and cache them in our servers. It’s impractical to keep updating the social share count for the 100,000,000+ articles in our database in real-time. Essentially, it’s the same reason why Google toolbar’s Pagerank, or Moz’s Page Authority is not updated real-time.
However, we do update most article’s share counts on a weekly, and monthly basis, so the discrepancies should be low. We find that most pieces of content gets shared a lot in the first few days, and then gradually stops being shared.